There have been proposed different combustible gas supply systems to an engine. In a known system, the gas output by a reducer-vaporiser is sent to a distributor-metering unit connected to the intake conduits of the various cylinders by way of respective conduits. The combustible gas is sent to the intake conduit of each cylinder by a solenoid valve assembly in which the shutter of each solenoid valve is carried by an armature of an electromagnet. The armature of the electromagnet is formed by an oblong plate that rotates about a contact line with one edge of a fixed element. Such contact is ensured by a bar of elastic material acting on one end of the armature. The armature, however, is held in closed position by a spring acting at the shutter.
These solenoid valves present some functional limits. First, the position of the contact line on the armature may vary due to the machining and assembly tolerance of the parts. Furthermore, the presence of the solenoid valve closing spring makes the operation of the latter relatively slow. Finally, the manufacturing of the solenoid valve is relatively costly, and the assembly and maintenance are particularly complicated.
A solenoid valve assembly for a combustible gas supply device comprising a solenoid valve having a shutter carried by a plate turnable about a contact line with a fixed element has also been proposed. This contact line consists of an edge formed by a slanted plane portion on a face of the plate, which is held in closed position by a bar of elastic material acting at the slanted plane portion. To maximize the amount of gas supplied, two selectively operable different solenoid valves are envisaged for each cylinder of the engine.
This solenoid valve assembly, in the case of an oily fluid such as LPG type gas, presents the drawback that the oil becomes very viscous at low temperatures, for example at −40° C. As a consequence, the gas supply of this assembly becomes problematic. Furthermore, at low temperatures, the elastic features of the returning bar are reduced, causing the armature to be returned to closed position with great delay. The elastic bar provides in all cases a non constant force for the detachment of the armature from the polar surface of the electromagnet core at various temperatures of use. Finally, the presence of two solenoid valves for each engine cylinder makes the device cumbersome and costly.